Secondary Electrohydrodynamic Flow Generated by Corona and Dielectric Barrier Discharges

One of the main goals of applied electrostatics engineering is to discover new perspectives in a wide range of research areas. Controlling the fluid media through electrostatic forces has brought new important scientific and industrial applications. Electric field induced flows, or electrohydrodynamics (EHD), have shown promise in the field of fluid dynamics. Although numerous EHD applications have been explored and extensively studied so far, most of the works are either experimental studies, which are not capable to explain the in depth physics of the phenomena, or detailed analytical studies, which are not time effective. The focus of this study is to provide the model that in a reasonable computational time is able to give us accurate results in different electric-fluid interactions. So, the main goals of this study is to provide a model to simulate all essential physical phenomena, applicable in different EHD systems. So, in this thesis, first, a two-dimensional numerical solver is presented for the dynamic simulation of the Dielectric Barrier Discharge (DBD) and the Corona Discharge (CD) in point to plane configuration. The simulations start with the single-species model and the different steps of the numerical technique are tested for this simplified model. The ability of the technique to model the expected physical behavior of ions and electric field is investigated. The studied physics were implemented in different geometry configurations such as wire to plane, wire to wire, and plane to plane geometries. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a Finite Element method (FEM). The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Then, the technique is applied to a more complicated model in order to address several existing EHD applications. The complicated mutual interaction between the three coexisting phenomena of electrostatic field, the charge transport, and fluid dynamics, which affect the EHD process, were taken into account in all the simulations. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes (RANS) equations using FEM. The turbulence effect was included by using the k-ε model included in commercial COMSOL software. An additional source term was added to the gas flow equation to include the effect of the electrostatic body force. In all the simulations, the effects of different parameters on the overall performance of the system and its characteristics are investigated. In some cases, the simulation results were compared with the existing experimental data published in literature

Three-Dimensional Modeling of Electrostatic Precipitator Using Hybrid Finite Element - Flux Corrected Transport Technique

This thesis presents the results of a three-dimensional simulation of the entire precipitation process inside a single-electrode one-stage electrostatic precipitator (ESP). The model was designed to predict the motion of ions, gas and solid particles. The precipitator consists of two parallel grounded collecting plates with a corona electrode mounted at the center, parallel to the plates and excited with a high dc voltage. The complex mutual interaction between the three coexisting phenomena of electrostatic field, fluid dynamics and the particulate transport, which affect the ESP process, were taken into account in all the simulations. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a hybrid Finite Element (FEM) - Flux Corrected Transport (FCT) method. The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes equations using the commercial FLUENT 6.2 software, which is based on the Finite Volume Method (FVM). The turbulence effect was included by using the k-ε model included in FLUENT. An additional source term was added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations, using the User-Defined-Function (UDF) feature of FLUENT. The particle phase was simulated using a Lagrangian-type Discrete Random Walk (DRW) model, where a large number of particles charged by combined field and diffusion charging mechanisms was traced with their motion affected by electrostatic and aerodynamic forces in turbulent flow using the Discrete Phase Model (DPM) and programming UDFs in FLUENT. The airflow patterns under the influence of electrohydrodynamic (EHD) secondary flow and external flows, particle charging and deposition along the channel, and ESP performance in removal of submicron particulates were compared for smooth and spiked discharge electrode configurations in the parallel plate precipitator assuming various particle concentrations at the inlet. Finally, a laboratory scale wire-cylinder ESP to collect conductive submicron diesel particles was modeled. The influence of different inlet gas velocities and excitation voltages on the particle migration velocity and precipitation performance were investigated. In some cases, the simulation results were compared with the existing experimental data published in literature

Numerical studies of Electrohydrodynamic Flow Induced by Corona and Dielectric Barrier Discharges

Electrohyrodynamic (EHD) flow produced by gas discharges allows the control of airflow through electrostatic forces. Various promising applications of EHD can be considered, but this requires a deeper understanding of the physical mechanisms involved. This thesis investigates the EHD flow generated by three forms of gas discharge. First, a multiple pin-plate EHD dryer associated with the positive corona discharge is studied using a stationary model. Second, the dynamics of a dielectric barrier discharge (DBD) plasma actuator is simulated with a time-dependent solver. Third, different configurations of the extended DBD are explored to enhance the EHD flow. The results of the numerical simulations include the discharge current, space and surface charges, velocity profiles, EHD force and efficiency, which have been validated with the experimental data from collaborating researchers and those available in literature. This thesis provides a valuable insight into the physics of the EHD flow induced by gas discharge

EHD Turbulence in Channel Flows with Inhomogeneous Electrical Fields: A One-Dimensional Turbulence Study

Electricly enhanced flows can be found in various technical applications as, for example, in air cleaning devices and liquid metal or redox flow batteries. For both examples mentioned it is crucial to develop a general understanding of the relevant physical processes and model them economically. Additionally, a correct upscaling procedure is specifically relevant for the transition into the industrial scale. All of these aspects are challenging because of the multiscale and multiphysics nature of these flows. In this paper we present a lower-order modeling strategy that aims to bridge the gap between fundamental research and applications by utilizing stochastic one-dimensional turbulence (ODT). Two case studies are performed. One is for two-way coupled turbulent Couette flow of electrolytes and another for one-way coupled planar Poiseuille flow in a wire-plate electrostatic precipitator. By comparison with reference data, we show that the modeling approach is robust and has predictive capabilities. Nevertheless, we also discuss some limitations of the purely one-dimensional and stochastic dynamical representation

Plasma Processes for Renewable Energy Technologies

The use of renewable energy is an effective solution for the prevention of global warming. On the other hand, environmental plasmas are one of powerful means to solve global environmental problems on nitrogen oxides, (NOx), sulfur oxides (SOx), particulate matter (PM), volatile organic compounds (VOC), and carbon dioxides (CO2) in the atmosphere. By combining both technologies, we can develop an extremely effective environmental improvement technology. Based on this background, a Special Issue of the journal Energies on plasma processes for renewable energy technologies is planned. On the issue, we focus on environment plasma technologies that can effectively utilize renewable electric energy sources, such as photovoltaic power generation, biofuel power generation, wind turbine power generation, etc. However, any latest research results on plasma environmental improvement processes are welcome for submission. We are looking, among others, for papers on the following technical subjects in which either plasma can use renewable energy sources or can be used for renewable energy technologies: Plasma decomposition technology of harmful gases, such as the plasma denitrification method; Plasma removal technology of harmful particles, such as electrostatic precipitation; Plasma decomposition technology of harmful substances in liquid, such as gas–liquid interfacial plasma; Plasma-enhanced flow induction and heat transfer enhancement technologies, such as ionic wind device and plasma actuator; Plasma-enhanced combustion and fuel reforming; Other environment plasma technologies

Characterisation of electrohydrodynamic fluid accelerators comprising highly asymmetric high voltage electrode geometries

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.Electrohydrodynamics (EHD) is a promising research field with several trending applications. Even though the phenomenon was first observed centuries ago, there is very little research until the middle 20th century, as the mechanisms behind it were very poorly understood. To this date, the majority of research is based on the development of empirical models and the presentation of laboratory experiments. This work begins with an extensive literature review on the phenomenon, clarifying conflicts between researchers throughout the history and listing the findings of the latest research. The literature review reveals that there are very few mathematical models describing even the most important parameters of the EHD fluid flow and most are either empirical or greatly simplified. As such, practical mathematical models for the assessment of all primary performance characteristics describing EHD fluid accelerators (Voltage Potential, Electric Field Intensity, Corona Discharge Current and Fluid Velocity) were developed and are begin presented in this work. These cover all configurations where the emitter faces a plane or another identical electrode and has a cylindrical surface. For configurations where the emitter faces a plane or another identical electrode and has a spherical surface, Corona Discharge Current and Fluid Velocity models have been presented as well. Laboratory experiments and computer simulations were performed and are being thoroughly presented in Chapter 4, verifying the accuracy and usability of the developed mathematical models. The laboratory experiments were performed using two of the most popular EHD electrode configurations - wire-plane and needle-grid. Finally, the findings of this research are being summarized in the conclusion, alongside with suggestions for future research. The step-by-step development of the equipotential lines mathematical model is presented in Appendix A. Appendix B covers the mathematical proof that the proposed field lines model is accurate and that the arcs are perpendicular to the surface of the electrodes and to all of the equipotential lines

Electrohydrodynamic Driven Airflows for Microelectronics Thermal Management

The increasing demand for effective and compact thermal solutions for the next generation of thin and high-power density consumer electronics is challenging the capability of miniature mechanical systems to meet the required cooling performance. Due to their attractive and unique advantages with no moving parts, design flexibility, small-scale structure, low height profile, silent operation, and effective flow generation, electrohydrodynamic (EHD) air movers are well positioned to become a key emerging cooling technology as alternative to conventional rotary fans. In its general objective, this thesis aims to investigate the benefits and highlight the features of EHD air movers as a thermal management cooling solution in advanced and small-scale microelectronics, supporting all previous efforts in this direction. Due to the strong influence of the geometric parameters of EHD devices on the corona discharge process and the resulting EHD flow, numerical modelling represents a powerful tool to design and optimize EHD devices, especially of complex and small-scale structures, where the capability of experimental investigations is limited or challenging. This study presents an accurate and validated numerical method to solve the coupled equations of electrostatics, charge transport and fluid flow for the two-dimensional (2D) modelling of EHD airflow induced through a wire-to-plane/grid channel configuration, and is the first to develop a three-dimensional model (3D) that couples the EHD flows with conjugate heat transfer modelling. Based on thermal management requirements and from a design perspective, a comprehensive investigation and analysis into the influence of geometric parameters on the efficiency of EHD wire-to-grid blowers is performed and optimal configurations are proposed for a range of heights from 9 to 15 mm. Results reveal that using fine emitter wires is more efficient than thicker ones, and the grounded electrode locations affect significantly the electric field distribution and the blower efficiency. It is also found that using the grid as a further collector increases the blower performance, with higher flow production, lower operating voltage and reduced blower size. Further numerical developments are devoted to optimize the configuration of miniature wire-to-plane EHD blowers for heights up to 10 mm, which is the most preferred geometry for integration in the cooling systems of thin electronic applications. For ranges of fixed operating power and voltage, the efficient optimized electrode gaps are predicted and defined by simple expressions. The influence of channel sidewall on the EHD flow rate and velocity profile are investigated and the results show that the 2D modelling is valid to effectively predict flow rates produced by wide and short EHD blowers compared to that obtained by 3D simulations. A combined EHD air blower that enables a reduction in the level of applied voltage and a control of flow production is developed. Performance comparisons against commercial rotary blowers demonstrate that the optimized miniature EHD blowers are more competitive for cooling miniaturized and extended heated surfaces based on blower size, flow rate with uniform velocity profile, and power consumption. A novel design of an EHD system integrated with compact heat sinks is presented as a thermal management cooling solution for advanced and thin consumer applications. Results of a parametric study demonstrate that the EHD system offers flexible structure design with the ability to reduce the height and increase the width as required, providing a unique feature to be installed in low-profile laptops. Moreover, compared to traditional cooling systems used in the current standard low power laptops, the proposed EHD system offers promising cooling performance with higher thermal design power (TDP), reduced thermal solution volume and lower height profile